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A transformer core includes: a plurality of core steel laminations; at
least one guide slot on a surface of steel sheet forming each of the
plurality of core steel laminations; and at least one shape retainer
attached to the at least one guide slot joining a plurality of the steel
sheets together.

Inventors:

LEE; Seungwook; (Anyang-si, KR)

Applicant:

Name

City

State

Country

Type

LSIS CO., LTD.

Anyang-si

KR

Assignee:

LSIS CO., LTD.Anyang-siKR

Family ID:

1000001638328

Appl. No.:

14/986227

Filed:

December 31, 2015

Current U.S. Class:

1/1

Current CPC Class:

H01F 3/02 20130101

International Class:

H01F 3/02 20060101 H01F003/02

Foreign Application Data

Date

Code

Application Number

Apr 23, 2015

KR

10-2015-0057300

Claims

1. A laminated transformer core comprising: a plurality of core steel
laminations; at least one guide slot on a surface of steel sheet forming
each of the plurality of core steel laminations; and at least one shape
retainer attached to the at least one guide slot joining a plurality of
the steel sheets together.

2. The laminated transformer core of claim 1, wherein the at least one
guide slot is formed at a place where any change of magnetic flux density
of the steel sheet is minimized when currents flow the laminated
transformer core.

3. The laminated transformer core of claim 2, wherein the at least one
guide slot is formed at an outer peripheral side of the laminated
transformer core.

4. The laminated transformer core of claim 1, wherein the at least guide
slot has a curved shape or a polygonal shape.

5. The laminated transformer core of claim 1, wherein a number of guide
slots is proportional to a size of the each steel sheet where the at
least one guide slot is formed.

6. The laminated transformer core of claim 1, wherein each of the at
least one guide slot has the same shape as a traverse cross-section of
the shape retainer.

7. The laminated transformer core of claim 1, wherein the shape retainer
is separable from each of the at least one guide slot.

8. The laminated transformer core of claim 1, wherein a length of the
shape retainer is proportional to a thickness of each of the plurality of
core steel laminations.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] Pursuant to 35 U.S.C. .sctn.119(a), this application claims the
benefit of earlier filing date and right of priority to Korean Patent
Application No. 10-2015-0057300, filed on Apr. 23, 2015, the contents of
which are hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to a transformer core, an
integral part of distribution/transmission transformers used in power
systems, and more particularly, to a plurality of core steel laminations
of the transformer core and an assembling method of the plurality of core
steel laminations.

[0004] 2. Description of the Conventional Art

[0005] A transformer is a static machine having a core and two or more
windings wound on the core. Such a transformer transforms power from one
circuit to another without change frequency through electromagnetic
induction.

[0006] The electromagnetic induction produces an electromotive force
across a conductor exposed to time-varying magnetic fields. And most
transformers are used to increase or decrease the voltages of alternating
current in electric power applications.

[0007] For large power transformers, the transformer cores are assembled
by arranging a plurality of core steel laminations. And each of the
plurality of core steel laminations comprises multiple steel sheets
having a silicon content of 3 to 4% and a thickness of 0.23 to 0.35 mm.

[0008] In general, such a laminated core of a large-capacity transformer
has about 1,000 mm thickness or greater thickness than 1,000 mm. It thus
requires stacking of several thousands of silicon steel sheets with 0.23
to 0.35 mm thickness. And, for facilitating the stacking of those silicon
steel sheets, one or more holes used to be drilled in the each of the
silicon steel sheets depending on manufacturing needs.

[0009] FIG. 1 illustrates an example of a conventional transformer core
100 under assembly to form a finished transformer core for large power
transformers.

[0011] For instance, when the laminated core is completely assembled, the
core steel lamination 110 can be then a core bottom yoke. And a result of
this, the lamination 130 can be a core top yoke, and the laminations 120
and 140 can be a pair of legs that connect the core bottom yoke and the
core top yoke.

[0012] For building the laminated core 100, those four core steel
laminations 110,120,130, and 140 assembled in a stack are bound together
by various means.

[0013] FIG. 1 does not give details of how to assemble the four core steel
laminations. But, in FIGS. 2a, and 2b, the steel sheets 211 and 221 have
a splice joint such that each sheet's leading ends joined to the other
sheet's leading ends.

[0014] In FIG. 1, each of every steel sheets forming the core steel
laminations 110, 120, 130, and 140 has at least one hole at its surface
with a preset size respectively. For example, those holes indicate the
regions that the steel sheets to position 150 and 170 on the first core
steel lamination 110.

[0015] They also keep its lamination in shape while being assembled to
form a finished lamination shape. For the similar purpose of the quick
stacking, the second core steel lamination 120 consists of steel sheets
with a plurality of holes. And, those holes have an average diameter of
20 to 30 mm.

[0016] In FIG. 1, a plurality of arrow lines depicted on the steel sheets
illustrates an exemplary flows of the magnetic field when current flow
the windings (not indicated) wound on the core steel laminations 110,
120, 130, and 140.

[0017] Here, due to the holes, the magnetic flux is not fairly uniform
throughout an entire surface of the steel sheet. More precisely, the
magnetic flux lines adjacent to the holes are more concentrated than the
other regions remote from the holes. And such distorted magnetic flux
distribution reduces the transformer's electrical performance.

[0018] As shown in FIG. 1, those drilled holes occupy the material of the
steel sheet such that it reduces the stacking factor of the core. In
addition, a burr is formed while punching a stacking hole in each steel
sheet.

[0019] The burr forms gaps between the stacked steel sheets, thus causing
a decrease in the stacking factor of the core. Also, the transformer core
with the staking holes produces noise when an alternating current (AC)
flows the windings wound on the core. The gaps between each of the
stacked steel sheets make the bigger vibration noises.

[0020] To solve those technical problems, a method using a hollow
container to cover the core steel lamination is proposed for quickly and
safely stacking a plurality of one or more than one sheets of core steel
materials forming the core steel lamination.

[0021] However this method is partially effective because it only
eliminates the need of the holes fixing the steel sheet of the
lamination. The problem is that making the shape of the hollow container
corresponding to a unique shape of the transformer core steel lamination,
e.g., a pot-belly shape, is simply a difficult and time and cost
consuming task.

SUMMARY OF THE INVENTION

[0022] The present invention has been made to solve the problems mentioned
above. A shape retainer is employed to facilitate assembling the core
steel laminations.

[0023] The shape retainer is fixed or attached to the laminated core
through a respective guide slot such that the guide slot does not reduce
the desired electromagnetic feature of the core steel laminations.

[0024] The one or more shape retainers attached to the core steel
lamination improve the stacking factor of the laminated core and reduce
vibration noises coming from the conventional holes. Those retainers are
also effective in preventing a temperature increase due to the use of the
conventional transformer core.

[0025] In addition, the respective guide slot to receive the shape
retainer locates at the place with the weakest strength of magnetic field
intensity.

[0026] Thus, the attachment of the shape retainer to the guild slots is
effective in minimizing the variations in the magnetic flux density of
the steel sheet surface that caused by the conventional stacking holes,
thus improving the transformer performance.

[0027] An exemplary embodiment of the present invention provides a
laminated transformer core comprising: a plurality of core steel
laminations; at least one guide slot on a surface of steel sheet forming
each of the plurality of core steel lamination; and at least one shape
retainer attached to the at least one guide slot joining a plurality of
the steel sheets together.

[0028] In this case, the at least one guide slot is formed at a place
where any change of the magnetic flux density of the steel sheet is
minimized when current flow the laminated transformer core.

[0029] In the case, the at least one guide slot is formed at an outer
peripheral side of the laminated transformer core.

[0030] In this case, the at least guide slot has a curved shape or a
polygonal shape.

[0031] In this case, a number of guide slots is proportional to a size of
the each steel sheet where the at least one guide slot is formed.

[0032] In this case, each of the at least one guide slot has the same
shape as a traverse cross-section of the shape retainer.

[0033] In this case, the shape retainer is separable from each of the at
least one guide slot.

[0034] In this case, the length of the shape retainer is proportional to a
thickness of each of the plurality of core steel laminations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and constitute a
part of this specification, illustrate exemplary embodiments and together
with the description serve to explain the principles of the invention.

[0036] In the drawings:

[0037] FIG. 1 is a cross-sectional view illustrating an example of a
conventional transformer core;

[0038] FIG. 2A is a cross-sectional view illustrating a transformer
according to an exemplary embodiment of the present invention;

[0039] FIG. 2B is a cross-sectional view showing a joint of steel sheets
of a transformer according to the present invention;

[0040] FIG. 3 is a cross-sectional view illustrating examples of a guide
slot and a shape retainer according to the present invention; and

[0041] FIG. 4 is a flowchart showing a process of stacking steel sheets of
a transformer core according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0042] Hereinafter, a laminated transformer core structure and a
manufacturing method thereof according to the present invention will be
described in detail with reference to the accompanying drawings.

[0043] Referring to FIG. 2A, a transformer core 200 according to an
exemplary embodiment of the present invention is illustrated. The
laminated transformer core 200 has four core steel laminations 210, 220,
230, and 240. The four steel laminations 210, 220, 230, and 240 are made
of a plurality of thin steel sheets stacked in the thickness direction of
the transformer core 200.

[0044] Shape retainers 250,260,270 and 280 are implanted in the middle of
the edges of the four steel laminations 210, 220, 230, and 240
respectively. The shape retainers 250, 260,270, and 280 stand in the
thickness direction of the transformer core 200 or perpendicular to the
ground.

[0045] The length of those shape retainers is set as proportional to the
thickness of the core steel laminations 210, 220, 230, and 240, and can
be varied by other technical needs.

[0046] With the use of the shape retainers 250, 260, 270, and 280, the
thin steel sheets 211, 221, 231, and 241 are quickly stacked on their
corresponding core steel laminations 210, 220, 230, and 240. And the
shape retainers embodied to the partially assembled core steel
laminations help keep the core in its shape while forming a complete
shape of the core 200.

[0047] As shown in FIG. 2A, the plurality of guide slots 211a, 221a, 231a,
and 241a can be arranged at the outer edges of the steel sheets 211, 221,
231, and 241. Their locations are defined in that the guide slots avoid
the path of the magnetic flux flow. Thus, when a current flows the
windings (not shown) wound on the transformer core 200, any change of
density of magnetic field lines, which is expected to occur by the holes
(guide slots), can be minimized. That is, the guide slots occupy any
place in the steel sheet that does not affect the original flux density.

[0048] When the core is under assembly, the retainers 250,260, 270 and 280
implanted in the core can facilitate the placement of the steel sheets
and easy assembling. The shape retainers fill the guide slots 211a, 221a,
231a, and 241a respectively. And, the filled slots can minimize any
variations in the magnetic flux density of the steel sheets that used to
be caused by the stacking holes as s discussed above.

[0049] As an example of the present invention, the material of the shape
retainer can be the same as the silicon steel sheets.

[0050] As an example of the present invention, the shape retainers 250,
260, 270, and 280 can be separable from the guide slots 211a, 221a, 231a,
and 241a.

[0051] The shape and number of guide slots 211a, 221a, 231a and 241a are
determined by taking into account factors, such as the easiness of
manufacturing a transformer core, reduction of transformer noises, and
variations in magnetic flux density.

[0052] The number of guide slots may be proportional to the area of the
steel sheet where the guide slots are to be formed. The number of the
guide slots is also determined by considering the breadth of the core
steel laminations 210, 220, 230, and 240 of the core, the height of the
core 200, and the like.

[0053] The length (h) of the shape retainer 250, 260, 270, and 280 is
determined by the user's technical needs.

[0054] As shown in FIG. 2B, the steel sheets 211, 221, 231, and 241 may
have a splice joint such that each steel sheet's leading ends are joined
to the other sheet's leading ends.

[0055] FIG. 3 illustrates the shapes of a guide slot formed in a steel
sheet and the shapes of a shape retainer attached to the guide slot as an
embodiment of the present invention.

[0056] As an exemplary embodiment of the present invention, a steel sheet
300 of the transformer core 200 have a wedge-shaped shape retainer 320
and a wedge-shaped guide slot 310 to receive the insertion of the
wedge-shaped retainer 320.

[0057] In another exemplary embodiment of the present invention, the steel
sheet 300 of the transformer core 200 have a rectangular-shaped shape
retainer 350 and a rectangular-shaped guide slot 340 to receive the
insertion of rectangular-shaped shape retainer 350.

[0058] However, the shape of a guide slot and the shape of a shape
retainer and the guide slot are not limited to the shapes mentioned
above. That is, the guide slot in the steel sheet may form a curved
shape, and the shape retainer attached to the curved guide slot may have
the same curved shape, depending other technical needs.

[0059] One or more guide slots may have the aforementioned specific shape
based on the area of the steel sheet where the guide slots form. Also,
the shape retainer according to the present invention can be made of the
material that can be easily manufactured.

[0060] FIG. 4 shows the process of making a transformer core according to
the present invention.

[0061] The first step is the step S1: forming one or more guide slots on a
plurality of steel sheets forming the transformer core 200. The guide
slot forms at one or more regions that bringing the least effects on the
magnetic flux density of a first steel sheet when a current flows in a
completed transformer core 200. The shape and number of guide slots are
determined by considering technical issues including the easiness of
manufacture of the core, the reduction of transformer noise, and the
improvement of the stacking factor of the core.

[0062] The second step is the step S2: assembling a shape retainer and a
first of the plurality of steel sheets. When the shape retainer is
inserted into the guide slot, the entire surface of the steel sheet can
be flat. Thus, the holes oriented non-uniformity of magnetic flux density
on the steel sheet can be eliminated. The shape retainer can be made of a
material that allows the length of the shape retainer to be easily
adjusted in alignment with the core stack.

[0063] The third step is the step S3: stacking a second of the plurality
of steel sheets on the first steel sheet through the shaper retainer that
stands perpendicular to the ground. By using the shape retainer, the
transformer core may be manufactured at a substantial time saving.

[0064] The fourth step is the step of S4: continuing the stacking up the
steel sheets to form a finished transformer core.